1. Field of the Invention
The present invention relates to measuring apparatus and method of measuring sound arrival delay time from a speaker to a microphone on the basis of a result obtained by collecting a signal output from the speaker by means of the microphone. In addition, the invention relates to a sound signal processing apparatus having a function of measuring the sound arrival delay time.
2. Description of the Related Art
In the related art, particularly in an audio system that outputs audio signals through multi-channels, a method has been known in which a test signal, such as a sine wave signal or a TSP (time stretched pulse) signal, is output from a speaker and the test signal is collected by a microphone that is separately provided, and on the basis of a result of the collected signal, delay time (sound arrival delay time) until a sound output from the speaker arrives at the microphone is measured.
FIGS. 13A and 13B illustrate an example of the method described above.
Here, in FIGS. 13A and 13B, a case of using a sine wave signal as the test signal is shown.
First, referring to FIG. 13A, a sine wave signal having a predetermined frequency is output as an output signal, which is shown in the drawing, from a speaker (point of time t1).
At a point of time t2, which is located apart from the output start point t1 of the sine wave signal by a predetermined period of time, the sine wave signal starts to be collected by a microphone, which is shown as a collected signal in the drawing. That is, a period of time between these points of time t1 and t2 is the sound arrival delay time until a sound output from the speaker arrives at the microphone (actual delay time in the drawing).
In addition, as an actual measuring operation, first, as shown as an input signal for measurement in the drawing, for example, input of the collected signal starts at a timing synchronized with a start timing of one period of the output signal (point of time t3). The input of the collected signal is performed during a predetermined period of time that is set beforehand. For example, in this case, the sine wave signal is input during one period, as shown in the drawing.
Here, assuming that the distance between the speaker and the microphone is zero, a waveform of the output signal becomes the same as that of the collected signal, the input of the collected signal being started in synchronization with the start timing of the output signal as described above. This is because, if the distance between the speaker and the microphone is zero, the beginning position (0-th clock) of an input signal should be the start position of a waveform of the input signal.
In other words, if the distance between the speaker and the microphone is not zero, the start position of the waveform of the input signal will be obtained by shifting the waveform of the input signal from the 0-th clock. Therefore, if the collected signal is input by making an input start timing synchronized with a start timing of one period of an output signal (that is, the start position of a waveform of an output signal), it is possible to measure the sound arrival delay time by examining how far the start position of the waveform of the input signal is from the 0-th clock.
That is, referring to FIG. 13A, a 0-th clock of the input signal corresponds to the point of time t3 and the start position of the waveform of the input signal corresponds to the point of time t4. Accordingly, it is possible to measure the sound arrival delay time by measuring a period of time between the points of time t3 and t4.
In the above-described method of measuring the delay time, it may be considered that the delay time is measured on the basis of a phase difference between the output signal and the collected signal.
However, in the measuring method described above, there is a limit that the delay time is measured, at the most, up to only a range not exceeding one period length of a sine wave signal.
FIG. 13B illustrates an example in which delay time is longer than one period length of a sine wave signal. In the case in which the delay time is longer than one period, since it is not possible to check to which period the start position of an input waveform corresponds, the delay time cannot be properly measured. In the example shown in FIG. 13B, the delay time measured corresponding to actual delay time (between points of time t1 and t10) is a period of time between points of time t11 and t12 indicating the phase difference between the output signal and the collected signal.
Therefore, in a method of the related art in which the sine wave signal is used, the delay time cannot be properly measured if the delay time is not within a range of one period length. In other words, in the method of using the sine wave signal described above, one period length (that is, frequency) of a sine wave signal is selected depending on the distance between a speaker and a microphone, which are objects to be measured, such that the delay time can be measured.
In addition, the related art includes JP-A-2003-061199 and JP-A-2005-236502.